1. Technical Field
The present application relates to a writing instrument, and more particularly to a fillerless writing instrument having a venting mechanism.
2. Background of Related Art
Baffle or fin-type venting mechanisms are common to writing instruments. These mechanisms are typically used in fillerless-type writing instruments to prevent ink leakage at varying ambient temperatures. Typically, filler-type writing instruments incorporate a porous filler material for containing the ink supply, whereas fillerless writing instruments incorporate an ink reservoir in combination with an ink transport system to carry the ink from the reservoir to the writing point.
Fillerless writing instruments exhibit several advantages over filler-type writing instruments. These advantages include an improved ink flow over the life of the writing instrument, and a greater utilization of the ink charge. For example, in filler-type writing instruments, often a substantial portion of the ink charge can be wasted as a result of the ink retention properties of the filler material. With fillerless writing instruments, most of the ink is usable and control of the usage is significantly better than with filler-type instruments.
There have been numerous attempts to manufacture a fillerless writing instrument. For example, U.S. Pat. No. 4,671,692 to Inaba discloses a writing pen having a flow-regulator having a labyrinth groove in its circumference interposed between a writing tip and an ink reservoir in a pen barrel in which an ink supply rod is inserted into the bore of the flow-regulator to guide ink to the writing tip. A body includes a labyrinth groove defined by a plurality of fins. A second ink supply rod made of porous material has a larger diameter than the first ink supply rod and guides ink to a third ink supply rod to thereby guide ink to the writing tip.
U.S. Pat. No. 4,382,707 to Anderka discloses a writing instrument having a single ink supply rod. This arrangement has several inherent disadvantages. For example, for an average sized writing instrument, the supply rod would necessarily be of significant length in order to feed ink directly from the ink reservoir to the writing point. To deliver ink to the writing point in specific amounts over such a great distance involves a loss of control and therefore may result in overfeeding or underfeeding the writing point with ink.
U.S. Pat. No. 4,239,408 to Mutschler discloses a writing instrument having an ink supply system having a flow controlling member, and an ink feeding member. The flow controlling member supplies ink from the reservoir to the ink feeding member. The ink feeding member supplies ink to the writing point. The flow controlling member has an effective flow section smaller than the flow section in the feeding member. Mutschler discloses a feed bar for venting ink having a spiral groove extending from the ink reservoir to an open orifice adjacent the point. However, the uniform nature of the groove does not provide structure to reduce the probability of excess ink entering the groove from flowing to the point.
The present invention relates to a writing instrument which avoids the above described disadvantages by providing first and second ink supply rods to provide a predetermined and consistent flow of ink as may be required. The writing instrument also incorporates structure to vent the ink supply to prevent the ink from leaking from the point of the writing instrument while enhancing the transport of ink with relative precision.